1. Field of the Invention
The present invention relates to a microwave cooker, and more particularly, to a microwave cooker capable of effectively preventing a microwave leakage by enhancing a microwave damping function.
2. Description of the Background Art
A microwave cooker such as a microwave oven, an electric oven, etc. serves to heat and cook food by scanning microwave generated from a magnetron to the food.
The microwave cooker generally comprises a body having a cooking chamber, and a door coupled to the body for opening and closing the cooking chamber. A gap is formed between the body and the door.
When microwave is leaked through the gap between the body and the door, the microwave does harm to a user's body. Therefore, a microwave leakage from the cooking chamber has to be prevented.
Various methods for preventing the microwave from being leaked from the cooking chamber through the gap between the body and the door have been proposed, in which a capacitive seal, a choke seal, or a ferrite rubber is installed between the body and the door.
The conventional method will be explained in more detail with reference to FIG. 1.
FIG. 1 is a graph showing a microwave damping curve of a microwave cooker in accordance with the conventional art, in which ‘A’ expressed as decibel (dB) denotes a damping degree according to a frequency (f) when the cooking chamber is closed.
In the conventional microwave cooker, a choke seal is formed at the door as a closed curve that surrounds a circumference of an opening of the cooking chamber of the body, and has a depth corresponding to ¼ of a wavelength in order to serve as a shielding portion of microwave. When the cooking chamber of the body is closed by the door, a resonant frequency (f-1) of the choke seal has the same frequency as a central frequency (f-MGT: magnetron) of microwave.
When the cooking chamber is opened, a microwave source for supplying microwave is turned off.
However, in the conventional microwave cooker, microwave is drastically leaked when the door is initially opened.
That is, before the microwave source is completely turned off, the door is opened for a certain section. As the gap between the body and the door is increased when the cooking chamber is initially opened, an electromagnetic characteristic is changed. Accordingly, as shown in FIG. 1, the microwave damping curve is moved to the left side, and thus a damping is performed at a region having an inferior damping function. Therefore, microwave is much leaked through the gap between the body and the door.
The U.S. Pat. No. 6,538,241 (hereinafter, will be referred to as the conventional microwave cooker) discloses a microwave sealing unit for stably performing a damping at a wide frequency region.
The microwave sealing unit has a double resonant structure having two sealing cavities, and a resonant frequency of each cavity is positioned at both sides of a central frequency of microwave. As each resonant frequency has a constant gap therebetween, a gap variation of the door is not greatly influential thereon and thus a damping function can be stably performed at a wide frequency region.
However, in the conventional microwave cooker, as each resonant frequency of the microwave sealing unit is spaced from each other in order to obtain a wide bandwidth, a damping function is lowered at a region between each resonant frequency. Furthermore, since a central frequency of microwave is positioned at a region having an inferior damping function, an optimum damping function of the microwave cooker is not implemented.
The wider a gap between each resonant frequency is (that is, the wider a bandwidth is), the lower a damping function between each resonant frequency is. Therefore, when the gap between the body and the door is more than approximately 4 mm, it is difficult to effectively prevent a microwave leakage.
In the conventional microwave cooker, odor, smoke, etc. generated from food inside the cooking chamber contaminate an inner surface of the door, especially, the choke seal or the microwave sealing unit, and the contaminated portion is not easily cleaned.